Embryonic stem cells are pluripotent cells capable of both proliferation in cell culture as well as differentiation towards a variety of lineage restricted cell populations that exhibit multipotent properties (Odorico et al., (2001) Stem Cells 19:193-204). Human embryonic stem (ES) cells are thus capable of commitment and differentiation to a variety of lineage-restricted paths resulting in very specific cell types that perform unique functions.
Generally, ES cells are highly homogeneous, exhibit the capacity for self-renewal, and have the ability to differentiate into any functional cell in the body. This self-renewal property can lead under appropriate conditions to a long-term proliferating capability with the potential for unlimited expansion in cell culture. Furthermore, it is understood, that if human ES cells are allowed to differentiate in an undirected fashion, a heterogeneous population of cells is obtained expressing markers for a plurality of different tissue types (WO 01/51616; Shamblott et al., (2001) Proc. Natl. Acad. Sci. U.S.A. 98:113). These features make these cells a unique homogeneous starting population for the production of cells having therapeutic utility.
There have been efforts by researchers in the field to develop methods to culture a variety of progeny cell types from human ES cells. For example, U.S. Pat. No. 6,280,718 describes a method for culturing human ES cells into hematopoietic cells by culturing the human ES cell with stromal cells. Some methods of creating progeny cell types from human ES cells involve the creation of embryoid bodies, which are three dimensional structures which can be formed by ES cells in culture and which foster the diverse differentiation of ES cells into various differentiated progeny lineages. Other methods for creating progeny lineages depend on the culturing of human ES cells with particular media, agents or types of cells to expose the ES cells to factors which encourage differentiation in a particular direction. All these methods have a common objective, which is to provide a source for particular cell types for scientific research and experimentation and, for some cell types, for ultimate transplantation into human bodies for therapeutic purposes.
Dendritic cells are immune cells that perform a critical function in the mammalian immune system. Dendritic cells (sometimes here DCs) are powerful antigen-presenting cells which are present at low frequency in tissues of the body in contact with the environment such as skin, and linings of the nose, lungs, stomach and intestines. Dendritic cells have the ability to uptake antigens and induce primary T cell responses to initiate generalized immune system responses to pathogens. Dendritic cells are so named because of their long processes or arms, called dendrites, that are characteristic of dendritic cell morphology.
Dendritic cells are generated continuously in the bone marrow from the hematopoietic lineage and mature in the blood. The dendritic cells of an individual have heterogeneous phenotype and function. Dendritic cells develop in several ways, and there may be differences among the dendritic cells depending on their lineage of derivation. Dendritic cells that develop from CD34+ hematopoietic progenitors along two independent pathways become Langerhans cells and interstitial dendritic cells. Dendritic cells derived from monocytes or from plasmocytoid T cells are referred to as monocyte-derived DCs or plasmocytoid DCs respectively. On the basis of their cellular origin phenotype, dendritic cells are normally classified broadly into two major divisions, myeloid or lymphoid. It was believed that myeloid DCs were developed from a common myeloid precursor while lymphoid DCs developed from a common lymphoid precursors, although it has now also been proposed that a common myeloid DC precursor gives rise to all dendritic cell lineages.
The availability of human immature dendritic cells would be useful for the study of antigen processing and presentation, as well as for understanding the mechanisms of the induction of immunity and tolerance. Functional analysis of human dendritic cell subsets was significantly facilitated by the development of in vitro systems for the differentiation of dendritic cells from CD34+ hematopoietic stem cells and monocytes. However, using these existing protocols, obtaining large numbers of human dendritic cell progenitors is a laborious process and is associated with potential risks for donors. Other aspects of dendritic cell biology, such as dendritic cell ontogeny, have not been studied in humans due to the difficulties in obtaining tissues during early development. The advent of human ES cells represents an opportunity to overcome these limitations.
Functional dendritic cells have been generated from mouse ES cells using embryoid bodies and by co-culture with mouse macrophage colony-stimulating factor deficient bone-marrow stromal cell line, OP9. We have previously demonstrated that OP9 cells can be used to induce hematopoietic cells from human ES cells. The full potency of those hematopoietic cells to produce progeny of the various lineages was unexplored previously.